1. Field of the Invention
The present invention relates to a process for treating exhaust gas generated within an electrophotographic machine which comprises making an odorous exhaust gas generated within the electrophotographic machine odorless, and an apparatus therefor.
2. Description of the Prior Art
Electrophotography is generally classified into wet and dry methods. In the former, a permanent image may be obtained through the steps of forming an electrostatic latent image on an image-bearing element such as a selenium electrophotographic element, a zinc oxide electrophotographic element or the like, developing the thus formed image with a liquid developer, transferring the developed image onto a transfer sheet as occasion demands, and thereafter heating and drying the developed or transferred image by means of a heating means such as heat roller or the like further as occasion demands. In the latter, on the other hand, a permanent image may be obtained through the steps of developing an electrostatic latent image formed in the same manner as described above with a powder developer (toner particles), transferring said image onto a transfer sheet as occasion demands, and thereafter thermally fixing the image by means of a heating means such as heat roller or the like. In addition, a method is also known which is designed to form an electrostatic latent image on an electrostatic recording element (which is also called a dielectric element) in place of an electrophotographic element. In this connection, it is to be noted that the electrophotographic element and electrostatic recording element shall hereinafter be called "an element being developed" respectively.
In the case of the wet method, an odorous solvent vapor-containing exhaust gas is discharged from a wet type electrophotographic machine utilizing this method, because the liquid developer used in the developing step contains a large quantity of solvent consisting essentially of a paraffinic or isoparaffinic hydrocarbon. This solvent vapor is caused mainly by evaporation of the solvent attached to the element being developed in the developing step or to the transfer sheet in the transferring step, but additionally by evaporation of the solvent attached to the developing unit or the like. This evaporation is more accelerated when the element being developed or transfer sheet is heated and dried in the drying step by means of a heating means.
Usually, such a solvent vapor-containing exhaust gas has been discharged to the outside of a machine without undergoing any treatment. Due to this, it has been called into question from the standpoint of environment sanitation that a small, especially confined room is filled with a high concentration of solvent gas in a short time in the cases of operating a machine at a high speed even when ventilating the room as well as operating the machine without ventilating the room. Therefore, various schemes to improve this problem have hitherto been proposed, for instance, (1) the use of a reversing squeeze roller for reducing the quantity of solvent attached to an element being developed and thereby suppressing the quantity of solvent vapor generated in the exhaust gas (which is disclosed, for instance, in U.S. Pat. No. 3,907,423 or German Pat. No. 2,361,833), (2) the introduction of exhaust gas (which has been collected by means of an air duct, this being applicable to the exhaust gas appearing hereinafter) to an adsorbent layer for allowing the gas to adsorb the solvent vapor, (3) the introduction of the exhaust gas into a high boiling solvent likewise for allowing said gas to adsorb the solvent vapor, (4) the passage of the exhaust gas through a condenser for removing a liquidified solvent vapor therefrom (which is disclosed, for instance, in U.S. Pat. No. 3,130,079), (5) the conversion of the solvent vapor contained in exhaust gas into a different substance through the reaction thereof with a reactive substance, and so forth. However, the scheme (1) still involves problems to be solved in image quality, that is, the resulting copy is of deteriorated image density and further the wide image area lacks the uniformity of image, the scheme (2) is defective in that the efficiency of adsorption is low, the scheme (3) is defective in that the efficiency of adsorption is more inferior than that of the scheme (2), the scheme (4) is defective in that the apparatus therefor becomes complicated and large-sized, which leads to high cost, and the scheme (5) has a problem to be solved in that a different odorous substance is created.
In the case of the dry method, on the other hand, an odorous gas is exhausted from an electrophotographic machine, too. The odorous substances contained in this exhaust gas, which are caused when the toner used is thermally fixed, are different in composition from those of the exhaust gas from the wet type electrophotographic machine, and in more detail comprise those generated from the toner particles and the electrophotographic element-constituting materials (various kinds of resins), for instance, such as the residual solvent, unreacted monomer and its decomposition gas and remaining solvent contained in the material resins and additionally those generated from the material constituting the surface of the heat roller (silicone resin), for instance, such as the remaining polymerization catalyst, silicone oil and the like. In either case, it is noted that these odorous substances are generated in a marked degree when using high-speed electrophotographic machines, in particular those wherein flash fixing is employed. In order to overcome the exhaust gases from these dry type electrophotographic machines, however, scarcely any counterplan has hitherto been considered likewise in the cases of wet type electrophotographic machines. The fact is that for that purpose there has only been proposed the adsorption method as described in the preceding (2) wherein active carbon is employed as an adsorbent. However, this method is defective in that because the active carbon has a short adsorbent life it will have to be exchanged earlier than usual and further that since air ducts required for collecting exhaust gases become large-sized electrophotographic machines per se will consequently have to become large-sized.